1. Field of the Invention
The present invention relates to inductively coupled plasma reactors for plasma processing, such as semiconductor wafer processing. More particularly, the invention relates to RF powered plasma etching, chemical vapor deposition, or plasma emission ion implantation using a vacuum chamber and an inductively coupled plasma.
2. Background of the Related Art
The fabrication of multiple layer semiconductor structures typically requires the selective etching of one material faster than another. If each layer can also contain three dimensional characteristics (i.e., a vertical etch profile), then anisotropic etching can be required. A sub-half micron polysilicon gate structure can, for example, require a vertical etch profile and an etching selectivity ratio of polysilicon to SiO.sub.2 of 50 or 100. Reactive chemical species of ions can provide high selectivity, but generally provide poor etch anisotropy. On the other hand, high energy ions can provide good anisotropy, but relatively poor selectivity. Extremely high selectivity and anisotropy in a plasma etch system require high density ions with very well controlled energy distribution. This has led to the development of high density plasma reactors.
For example, U.S. Pat. No. 5,540,800 issued on Jul. 30, 1996 and which is assigned to the assignee of the present invention, shows a high density plasma reactor having an RF inductively coupled plasma generator employing a transformer isolating RF antenna. While this design has proven very useful, the present invention is an improvement in operation over this design and is itself a simplified design.
In sputter etch processes, a gas such as argon is typically introduced into a chamber and a negative bias is capacitively coupled to a substrate or workpiece. The chamber walls are grounded and a plasma is struck in the space between the substrate and the chamber lid. The negative bias attracts the ions in the plasma causing a cascade of collisions of the ions with the substrate surface. As the ions collide with the substrate, material deposited on the surface of the substrate, such as SiO2, will be ejected or sputtered from the surface and deposit on the other chamber components or be exhausted from the chamber. This arrangement requires that a plasma be capacitively coupled within the chamber by placing the negative potential on the substrate and grounding the chamber walls. Capacitive sputter etching of substrate surfaces is a slow and inefficient process.
Therefore, there remains a need for an etchback process which is faster than capacitively coupled plasma process.